In small hearing aids which are to be worn in the ear, the distance between the antenna and the receiver or speaker will be small and as a result, the antenna is likely to pick up unwanted electromagnetic radiation. Inside the hearing aid a microphone and a receiver are placed along with a signal processing device and a battery. The receiver delivers a signal to the user which is perceivable as sound but at the same time the receiver will radiate electromagnetic energy and this is likely to be collected by the antenna and may give rise to either feedback problems or noise. Hearing aids of the above kind are often custom made and the location of electronic devices (the receiver and the signal processing device) within the casing may differ in different hearing aids. As the function of the antenna may depend on the location of nearby electric components it is a problem to not know the exact location of nearby components in advance as this may lead to antennas with widely varying performance in different hearing aids.
Today wireless communication at frequencies above approximately 1 MHz is not implemented in In-The-Ear (ITE) hearing aids. This will most likely change in the future, and then highly efficient antennas (compared to the available volume) will be needed in order to enable acceptable performance (range, current consumption, etc.). One patent application has been published in this area covering amongst others the use of the pull-out string as an antenna. U.S. Pat. No. 5,721,783 discloses a hearing aid or audio communication system includes an earpiece that can be hidden in the ear canal, and which communicates wirelessly with a remote processor unit, that enhances audio signals and can be concealed under clothing. The disclosed hearing aid has an antenna arranged in conjunction with the pull out string of the hearing aid.
In prior art document EP 1326302 an integrated circuit fractal antenna in a hearing aid device is disclosed. The fractal antenna can be incorporated in the hearing device to optimize wireless communication capabilities of the device.
EP 1013143 discloses a hearing aid comprising a detector for wireless reception of signals and a system comprising said hearing aid. The disclosed hearing aid accommodates an electronic circuit and a battery compartment. A faceplate includes a lid-shaped element which can be moved with respect to the battery compartment. A detector is secured to the lid-shaped element, which detector is embodied so as to be suitable for the wireless reception of signals and conversion thereof to electrical signals. The hearing aid is provided with an electrical connection means which, at least in the closed position of the lid-shaped element, connects the detector to the electronic circuit. The disclosed detector is used for the reception of signals in the infrared light range. As this known receptor works in the infrared light range, where the penetration depth of the signals is poor, it must be placed at an external surface part.
The antenna according to the present invention will be working in the radio frequency range, where the penetration depth of signals is grater, and it cannot in advance easily be determined what will be an advantageous position of the antenna. Further the sensitivity of a radio frequency antenna towards close by electronic components is a problem which has not been dealt with previously.